Field of the Invention
The present invention relates to a four-cycle OHV engine appropriate for such as an outboard motor that includes an internal combustion engine as a power source.
Description of the Related Art
In what is called a vertical engine where a crankshaft is vertically disposed, a lubricating system including an oil pump to pump lubricating oil includes a lubricating oil passage to circulate the lubricating oil. The lubricating system includes an oil filter, a drive mechanism of an oil pump and similar unit, and these units are connected to one another via a lubricating oil passage.
For example, in an engine disclosed in Patent Document 1, a main shaft of an oil pump extends upward to be integrally rotatingly coupled to a lower end of a balancer shaft. This causes the oil pump to be directly driven when the balancer shaft rotates. Thus the oil pump is driven by the balancer shaft other than a camshaft, includes an oil filter on a cylinder side portion, and uses the oil filter to return cleaned lubricating oil after filtration to a crankshaft.
Patent Document 1: Japanese Laid-open Patent Publication No. 10-47030
In the conventional vertical engine, the lubricating oil passage that supplies the lubricating oil after the filtration by the oil filter is not directly connected to the drive shaft of the oil pump. This makes the lubricating oil passage complicated. The lubricating oil passage for the camshaft is additionally required, and this makes the size of the engine large especially in the width direction. Accordingly, it has been an actual condition that such as downsizing of the engine is actually difficult.